Hi,

I am a new tranny tech, a customer of mine came to me with transmission that doesn't shift from D2 to D3 at wot and very harsh shifting all the time at all gears and ranges. i dismantled the transmission and found the following:

burned band and damaged input drum
wrong servo pin (broken and fixed by welding which made it longer)
very tight clearance of 3-4 clutch pack
oil PR tested and found leaking badly, replaced with over size and leak was fixed (tested by sonnax vacuum test kit)
VB was tested and found okay
manual lever switch was found faulty and replaced with new one.

the tranny was fixed, after testing the harsh shifting issue is resolved but the wot issue is not resolved

please advice if you know the cause.....

Thanks,

 

What vehicle is this in?

If going from a stock build to performance build could be a tuning issue.

Does it eventually shift after bouncing off the limiter?

 

The 2 - 3 and the 3 - 2 shifts in this unit are "syncronous shifts" and require proper clearances/ timings of the corresponding band and clutch assembly.

Should the 2 - 4 Band be too lose and the 3 - 4 clutch be too tight; the 2 - 3 up-shift will not occur properly (basically what you found).
Also should the 2 - 4 band be too tight and the 3 - 4 clutch be too lose... the 2 - 3 shift will still not occur properly.

Incorrect timing of this shift will either cause a down-shift into first instead of third; or up-shift into fourth instead of third, before eventually going into third gear.

This is going to go against what the GM factory specifications support. However, most of us builders even set up stock units with these specs that I am giving you.

2 - 4 Band clearance target: 0.060" ...Slightly more is okay (0.075'') Use the OEM Green Band
3 - 4 Clutch clearance target: 0.030" ...Slightly more is okay (0.045"). Use the OEM clutches with 4L65E H-D THICK apply and selective backing plates.

This clearances will give you the proper shift timings.

I would recommend installing a "Corvette" intermediate servo if the trans does not have one.
Install a new servo check-ball capsule. (If the trans is completely stock with no valve-body changes, then buy the Superior-Fairbanks version of the part).
Install a new sun-gear shell and gear if this unit is older than 2008 or if you see any ware.

 

thanks a lot for the advice, clearnce is made with in the range you mentioned. the car is 08.....

Thanks, the transmission is stock but was replaced at another shop before it came down to me with this issue.

 

by the way there is no DTC related to transmission. should i replace solenoid B ? or test it externally.

 

Install the sonnax HD 2-3 shift valve and remove checkball #6

When shifting a 4l60e from 2nd to 3rd manually, lots is happening.

in 2nd, you have the forwards holding and the band holding
in D3 you have the band releasing via oil filling the "backside" of the servo and pushing-off the band, the 3/4 engaging, the forwards holding, AND the overruns applying. Having to apply the overruns at the same time as the 3rd accum (backside servo) oil volume is filled...the 3/4 clutch volume is filled...that's alot. The overruns just act like a 2nd accumulator. No bueno

However...before you go tearing into the trans and changing anything...explain better how it's not making the shift. Is it banging off the limiter...is it "flaring"...is it "bogging"
If you leave the shifter in OD position, will it make a WOT 2-3?
when you vac tested the valve body...you're saying it was ALL good? no issues at all? If so...it's been serviced before or you've found a unicorn

 

thanks for your input, I will test it with shifter in OD position. when it doesn't shift the engine is hitting the rev limit no flaring at all.

I don't know if the VB was serviced before, all pistons of the VB are stock size. when i said okay I meant they are not lower than the min recommended values by sonnax.

I do have the 2-3 HD upgrade by sonnax, if it is going to resolved the issue I will install it .... as I know it makes the over run clutches engaged all the time in OD or D1/2/3

 

It does not apply the overruns in OD shifter position.
Just D1/D2/D3

See my explanation above for how the overruns act like another accumulator during a 2-3 shift in stock form.

Since it's just hitting the limiter...not slipping or flaring...have you doublechecked with a log or scanner that the shift is being commanded?
Have you performed a pressure test...especially during the shift?

 

regarding the log, it shows 3d in the current gear as well as the PRNDL status. i will post a log with the testing result today


regarding the pressure test, do you mean the one done during assembly ?

 

i do confirm that the car shifts normally at OD log is attached. I lowered the shifting point for testing only

however i am attaching logging files

 

The HD 2-3 shift valve is insttaled and checkball #6 removed too, still the same issue is there....

 

I'll have to look at the log later this evening. I don't have my tuning laptop with me at work today.
Post a tune file too if you can

 

here are both of them the stock as well as the last one in the car.... i made a lot of changes trying to resolve the issue...

 

3rd is a lil funky in a 60e setup. Usually has alot of delay before it completes the shift. 2nd not so bad.

What i do is set your max rpm rev limit for every gear to 7k. This will be under the Engine tab section.

In the trans section set your wot speed to stock settings. Or use gear wizard and let it auto adjust.

Set your commanded gear shift rpm to 6k. Thin see how it acts on a wot OD pull and report back.


U need to set the shift rpm early bc of the delay. Say u command 6k shift, it want actually make shift to 6800. Thts why i always set main max limiter to somthing high like 7k. Ive never had a car/truck bang the limiter before shift. They always need some head room. Hope this helps.

 

Thanks a lot for your input, the issue i have is different.

 

odd boy, shoot me a pm
I forgot to look at these over the weekend. I'll try to take a peek at lunch

 

Looking at the d3 and OD logs...you've got some funky stuff going on
In OD...3rd is being commanded at 47mph and 4450 rpm...but doesn't shift until 56mph and 5200 rpm. That's alot of delay
In D3 its being commanded at 63 mph. Your tunes have issues...the "normal" shift patterns 100% throttle mph should match the WOT tab mph.
But Once that shift is commanded...it should shift even in d3.

I would recommend using "bluecat's" shifting software to help you get the tune in the right spot.
But It appears as though the trans is very sluggish and not performing optimally either

 

I would flash back to stock settings and see how it does. Trans could have the 3-4s going out! Typical problem on the 60e